The present invention relates to improvements in pressure regulating methods and apparatus.
It is often necessary to design a hydraulic control system in such a way that a regulating or control valve (e.g., a pressure reducing valve) is installed downstream of a pilot valve or servo valve (hereinafter called pilot valve). The latter serves to select fluid pressure in a (pilot) conduit which is connected with an inlet of the regulating valve. An outlet of the regulating valve serves to convey fluid to one or more consumers, e.g., to a so-called continuously variable transmission (CVT). Reference may be had, for example, to commonly owned U.S. Pat. No. 5,667,448 (granted Sep. 16, 1997 to Oswald Friedmann for xe2x80x9cPOWER TRAINxe2x80x9d) and to commonly owned U.S. Pat. No. 5,674,155 (granted Oct. 7, 1997 to Dieter Otto et al. for xe2x80x9cMETHOD OF AND APPARATUS FOR TRANSMITTING TORQUE IN THE POWER TRAINS OF MOTOR VEHICLESxe2x80x9d). The disclosures of the just enumerated US patents as well as of all other patents and patent applications (including commonly owned pending German priority patent application Ser. No. 198 29 148.5 filed Jun. 30, 1998) are incorporated herein by reference.
A conventional pilot valve-regulating valve combination can employ a pilot valve having an inlet connected to a source of constant-pressure (or substantially constant-pressure) fluid by a constant-pressure conduit which contains a flow restrictor) e.g., an adjustable diaphragm, and can communicate with a pilot conduit serving to convey fluid to the regulating valve. An adjustable valving element of the pilot valve can divert varying quantities of fluid from the pilot conduit (downstream of the flow restrictor) to a sump or to another destination so that the pilot valve can select the pressure of fluid entering the body of the regulating valve.
A drawback of heretofore known pressure regulating methods and apparatus of the just outlined character is that (for example, due to often unavoidable leakage of fluid from the pilot valve and/or from other parts of the apparatus), the pressure in the pilot conduit (between the pilot valve and the regulating valve) cannot match the pressure of fluid in the constant-pressure conduit. Moreover, even if the valving element of the pilot valve is moved to a fully open position (in which the valving element does not interfere with the flow of fluid from the pilot conduit, through the pilot valve, and on to to the sump), the pilot pressure of fluid (in the pilot conduit) still exceeds zero pressure. Such residual pressure in the pilot conduit is attributable to losses developing in the region of the flow restrictor, e.g., to losses in the path defined by the constant-pressure conduit, by the flow restrictor, by a branch conduit connecting the constant-pressure conduit (downstream of the flow restrictor) to the inlet of the pilot valve, and by the conduit connecting the outlet of the pilot valve with the sump or with another receptacle for hydraulic fluid.
A further drawback of the aforedescribed conventional pressure regulating apparatus is that, due to turbulence which develops in the fluid path in the region of the flow restrictor, at least a high percentage of kinetic energy of the fluid (such as oil) is ultimately converted into heat.
An object of the invention is to provide a novel and improved method of regulating the pressure of hydraulic fluid which is utilized in cylinder-and-piston units and/or other constituents of transmissions and/or other fluid-operated components, e.g., in the power trains of motor vehicles.
Another object of the invention is to provide a method which can be practiced without the generation of appreciable, noticeable or even any quantities of heat.
A further object of the invention is to provide a method which can be practiced by resorting to a relatively simple, compact and inexpensive apparatus.
An additional object of the invention is to provide a method which renders it possible to reduce the pilot pressure between the pilot valve and the regulating valve of the appparatus to a threshold value below that achievable by resorting to heretofore known methods.
Still another object of the invention is to provide an apparatus which can be utilized for the practice of the above outlined method and is designed in such a way that the aforedescribed drawbacks of conventional apparatus can be avoided in a simple, effective and inexpensive manner.
A further object of the invention is to provide a novel and improved pilot valve-regulating valve combination for use in the above outlined apparatus.
Another object of the invention is to provide the improved apparatus with a novel combination of a flow restrictor and conduits for conveying hydraulic fluid from a source of fluid at an at least substantially constant pressure (e.g., from a valve) to the pilot valve and from the pilot valve to the regulating valve.
An additional object of the invention is to provide an apparatus which can be utilized in the power trains of motor vehicles as a superior substitute for the aforedescribed and other conventional pressure regulating apparatus.
Still another object of the invention is to provide a fluid-consuming or fluid-operated unit, such as a continuously operable transmission, which embodies an apparatus of the above outlined character.
A further object of the invention is to provide an apparatus which exhibits the advantages but does not embody the drawbacks of standard fluid pressure regulating apparatus utilizing combinations of pilot valves and regulating valves in the path of hydraulic fluid flow from a source of constant-pressure fluid to a consumer requiring fluid at two or more different pressures.
Another object of the invention is to provide a motor vehicle, such as a passenger car, having a power train embodying a unit which consumes or is operated by a hydraulic fluid and which receives hydraulic fluid from the above outlined apparatus in accordance with a method of the present invention.
One feature of the instant invention resides in the provision of a method of controlling the pressure of a hydraulic fluid (e.g., a fluid which includes or constitutes a lubricant such as oil) in a pilot conduit which receives fluid at an at least substantially constant pressure from a constant-pressure conduit by way of a flow restrictor and a pilot valve which is adjustable to permit outflow of fluid from the pilot conduit through a branch conduit at a variable rate and to thus lower the static pressure of fluid in the pilot conduit in response to increasing rate of fluid outflow from the pilot conduit. The improved method comprises the steps of (a) establishing for the flow of fluid from the pilot conduit to the pilot valve a path extending from the pilot conduit first through the flow restrictor and thereupon through the branch conduit into and through the pilot valve, and (b) varying the speed of the fluid flowing through the flow restrictor to thus influence the static pressure of fluid in the pilot conduit.
The speed varying step can include adjusting the pilot valve to select the rate of fluid flow from the branch conduit into the pilot valve. The fluid which is permitted to flow from the pilot conduit, through the branch conduit and through the pilot valve can be confined in (i.e., collected by) a suitable receptacle, e.g., in a sump.
Another feature of the invention resides in the provision of an apparatus for controlling the pressure of a hydraulic fluid, e.g., a transmission fluid, a lubricant or the like. The apparatus comprises a pilot valve having an inlet, an outlet and means for varying the rate of fluid flow from the inlet to the outlet, a source of constant-pressure hydraulic fluid including a first conduit having an outlet, a branch conduit connecting the outlet of the first conduit with the inlet of the pilot valve, a pilot conduit which is arranged to receive fluid from the branch conduit and wherein the static pressure of fluid decreases in response to increasing rate of fluid outflow from the pilot conduit, and a flow restrictor which establishes an evacuating path for the outflow of fluid from the pilot conduit into the branch conduit.
The flow restrictor is installed between the first conduit and the pilot conduit. The latter establishes a second path for the flow of fluid to at least one of the first conduit and the branch conduit; the evacuating path can be oriented in such a way that it crosses the second path.
In accordance with a presently preferred embodiment, the first conduit includes a portion which constitutes a portion of the pilot conduit (for example, such portions of the first and pilot conduits can be disposed back-to-back), and the flow restrictor is provided in such portion of the first conduit. The inlet of the branch conduit in such apparatus is positioned to receive fluid flowing along the evacuating path from the pilot conduit, through the flow restrictor and across the first conduit; the outlet of such branch conduit is connected with the inlet of the pilot vave. The dimensions of the just described branch conduit can be selected in such a way that its inlet has a first cross-sectional area and that the branch conduit further includes a portion adjacent the inlet of the branch conduit (e.g., extending all the way from the inlet of the branch conduit and to the inlet of the pilot valve) and having a second cross-sectional area greater than the first cross-sectional area.
The just described inlet and portion of the branch conduit constitute a means for opposing the development of turbulence (such as vortices) in the evacuating path.
The means for varying the rate of fluid flow from the inlet to the outlet of the pilot valve can include a valving element (e.g., a piston which is reciprocable in the housing or body of the pilot valve) and means for moving the valving element relative to the body of the pilot valve. The moving means can comprise at least one magnet, e.g., an electromagnet.
The orientation of the first conduit and the pilot conduit can be such that these conduits include portions which are at least substantially normal to the branch conduit. The latter can have at least one bend between the flow restrictor and the inlet of the pilot valve. Alternatively, the branch conduit can be a straight conduit having an inlet communicating with the pilot conduit and an outlet communicating with the inlet of the pilot valve.
The improved apparatus can further comprise a regulating valve having an inlet arranged to receive fluid from the pilot conduit and an outlet, a consumer of fluid, and a control conduit connecting the outlet of the regulating valve with at least one inlet of the consumer. For example, the consumer can comprise a transmission in the power train of a motor vehicle, e.g., a so-called continuously variable transmission (CVT). A typical example of a continuously variable transmission is a transmission employing two parallel shafts each of which carries an adjustable pulley, and an endless belt or chain which is trained over the pulleys. The fluid which is supplied by the regulating valve by way of the control conduit can be utilized to vary the ratio of the transmission and/or to select the extent of frictional engagement between the flanges of the adjustable pulleys and endless chain or belt.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The iproved apparatus itself, however, both as to its construction and its mode of operation, together with numerous additional features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.